Voltage ripple reduction in a power management circuit

ABSTRACT

Voltage ripple reduction in a power management circuit is disclosed. The power management circuit includes a power amplifier circuit configured to amplify a radio frequency (RF) signal based on a modulated voltage and an envelope tracking integrated circuit (ETIC) configured to provide the modulated voltage to the power amplifier circuit via a conductive path. Notably, an output impedance presenting at an input of the power amplifier circuit can interact with a modulated load current in the power amplifier circuit to create a voltage ripple in the modulated voltage to potentially cause an undesirable error in the RF signal. In this regard, a notch circuit is provided, preferably in the ETIC, to reduce the voltage ripple within a modulation bandwidth of the RF signal. As a result, it is possible to minimize the undesirable error, such as root-mean-square (RMS) error vector magnitude (EVM), within the modulation bandwidth of the RF signal.

RELATED APPLICATIONS

This application claims the benefit of U.S. provisional patent application Ser. No. 63/347,065, filed on May 31, 2022, the disclosure of which is hereby incorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

The technology of the disclosure relates generally to reducing voltage ripple in a modulated voltage in a power management circuit.

BACKGROUND

Fifth generation (5G) new radio (NR) (5G-NR) has been widely regarded as the next generation of wireless communication technology beyond the current third generation (3G) and fourth generation (4G) technologies. In this regard, a wireless communication device capable of supporting the 5G-NR wireless communication technology is expected to achieve higher data rates, improved coverage range, enhanced signaling efficiency, and reduced latency.

Downlink and uplink transmissions in a 5G-NR system are widely based on orthogonal frequency division multiplexing (OFDM) technology. In an OFDM based system, physical radio resources are divided into a number of subcarriers in a frequency domain and a number of OFDM symbols in a time domain. The subcarriers are orthogonally separated from each other by a subcarrier spacing (SCS). The OFDM symbols are separated from each other by a cyclic prefix (CP), which acts as a guard band to help overcome inter-symbol interference (ISI) between the OFDM symbols.

A radio frequency (RF) signal communicated in the OFDM based system is often modulated into multiple subcarriers in the frequency domain and multiple OFDM symbols in the time domain. The multiple subcarriers occupied by the RF signal collectively define a modulation bandwidth of the RF signal. The multiple OFDM symbols, on the other hand, define multiple time intervals during which the RF signal is communicated. In the 5G-NR system, the RF signal is typically modulated with a high modulation bandwidth in excess of 200 MHz (e.g., 1 GHz).

The duration of an OFDM symbol depends on the SCS and the modulation bandwidth. The table below (Table 1) provides some OFDM symbol durations, as defined by 3G partnership project (3GPP) standards for various SCSs and modulation bandwidths. Notably, the higher the modulation bandwidth is, the shorter the OFDM symbol duration will be. For example, when the SCS is 120 KHz and the modulation bandwidth is 400 MHz, the OFDM symbol duration is 8.93 μs.

TABLE 1 OFDM Symbol Modulation SCS CP Duration Bandwidth (KHz) (μs) (μs) (MHz) 15 4.69 71.43 50 30 2.34 35.71 100 60 1.17 17.86 200 120 0.59 8.93 400

Notably, the wireless communication device relies on a battery cell (e.g., Li-Ion battery) to power its operations and services. Despite recent advancement in battery technologies, the wireless communication device can run into a low battery situation from time to time. In this regard, it is desirable to prolong battery life concurrent to enabling fast voltage changes between the OFDM symbols.

SUMMARY

Embodiments of the disclosure relate to voltage ripple reduction in a power management circuit. The power management circuit includes a power amplifier circuit configured to amplify a radio frequency (RF) signal based on a modulated voltage and an envelope tracking integrated circuit (ETIC) configured to provide the modulated voltage to the power amplifier circuit via a conductive path. Notably, an output impedance (e.g., an inductive impedance associated with the ETIC and the conductive path) presenting at an input of the power amplifier circuit can interact with a modulated load current in the power amplifier circuit to create a voltage ripple in the modulated voltage to potentially cause an undesirable error in the RF signal. In this regard, a notch circuit is provided, preferably in the ETIC, to reduce the voltage ripple within a modulation bandwidth of the RF signal. As a result, it is possible to minimize the undesirable error, such as a root-mean-square (RMS) error vector magnitude (EVM), within the modulation bandwidth of the RF signal.

In one aspect, a power management circuit is provided. The power management circuit includes a power amplifier circuit. The power amplifier circuit is configured to amplify an RF signal based on a modulated voltage received at a power amplifier input. The modulated voltage received at the power amplifier input comprises a voltage ripple caused by an output impedance presenting at the power amplifier input and a load current induced by the modulated voltage. The power management circuit also includes an ETIC. The ETIC is coupled to the power amplifier input via a conductive path. The ETIC includes a voltage modulation circuit. The voltage modulation circuit is configured to generate the modulated voltage at a voltage output based on a modulated target voltage. The ETIC also includes a notch circuit. The notch circuit is coupled to the power amplifier input via a notch path. The notch circuit is configured to resonate at a notch frequency within a modulation bandwidth of the RF signal to reduce the voltage ripple to thereby achieve a defined performance threshold.

Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.

FIG. 1A is a schematic diagram of an exemplary existing transmission circuit wherein a power management circuit is configured to reduce a voltage ripple in a modulated voltage based on a conventional approach;

FIG. 1B is a schematic diagram of an exemplary electrical model of the power management circuit in FIG. 1A;

FIG. 1C is a graphic diagram providing an exemplary illustration of magnitude impedance as a function of modulation frequency;

FIG. 2 is a schematic diagram of an exemplary power management circuit configured according to an embodiment of the present disclosure to reduce a voltage ripple in a modulated voltage by reducing an output impedance presenting at a power amplifier input of a power amplifier circuit;

FIG. 3 is a schematic diagram providing an exemplary illustration of an inner structure of a voltage amplifier in the power management circuit of FIG. 2 ;

FIG. 4 is a schematic diagram of an exemplary power management circuit, wherein a notch circuit can be added to the power management circuit of FIG. 2 to further reduce the voltage ripple in the modulation voltage;

FIG. 5 is a schematic diagram illustrating an exemplary configuration of the notch circuit in FIG. 4 ; and

FIG. 6 is a schematic diagram of an exemplary user element wherein the power management circuits of FIGS. 2 and 4 can be provided.

DETAILED DESCRIPTION

The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.

It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present disclosure. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

It will be understood that when an element such as a layer, region, or substrate is referred to as being “on” or extending “onto” another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or extending “directly onto” another element, there are no intervening elements present. Likewise, it will be understood that when an element such as a layer, region, or substrate is referred to as being “over” or extending “over” another element, it can be directly over or extend directly over the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly over” or extending “directly over” another element, there are no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present.

Relative terms such as “below” or “above” or “upper” or “lower” or “horizontal” or “vertical” may be used herein to describe a relationship of one element, layer, or region to another element, layer, or region as illustrated in the Figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including” when used herein specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

Embodiments of the disclosure relate to voltage ripple reduction in a power management circuit. The power management circuit includes a power amplifier circuit configured to amplify a radio frequency (RF) signal based on a modulated voltage and an envelope tracking integrated circuit (ETIC) configured to provide the modulated voltage to the power amplifier circuit via a conductive path. Notably, an output impedance (e.g., an inductive impedance associated with the ETIC and the conductive path) presenting at an input of the power amplifier circuit can interact with a modulated load current in the power amplifier circuit to create a voltage ripple in the modulated voltage to potentially cause an undesirable error in the RF signal. In this regard, a notch circuit is provided, preferably in the ETIC, to reduce the voltage ripple within a modulation bandwidth of the RF signal. As a result, it is possible to minimize the undesirable error, such as a root-mean-square (RMS) error vector magnitude (EVM), within the modulation bandwidth of the RF signal.

Before discussing the specific voltage ripple reduction embodiment of the present disclosure, starting at FIG. 2 , a brief overview of an existing transmission circuit is first discussed with reference to FIGS. 1A-1C to help understand some issues related to reducing voltage ripple based on conventional approaches.

FIG. 1A is a schematic diagram of an exemplary existing transmission circuit 10 wherein a power management circuit 12 is configured to reduce a voltage ripple V_(CC-RP) in a modulated voltage V_(CC) based on a conventional approach. The power management circuit 12 includes an ETIC 14 and a power amplifier circuit 16. The ETIC 14 is configured to generate the modulated voltage V_(CC) based on a modulated target voltage V_(TGT) and provide the modulated voltage V_(CC) to the power amplifier circuit 16 via a conductive path 18 (e.g., a conductive trace), which is coupled between a voltage output 20 of the ETIC 14 and a power amplifier input 22 of the power amplifier circuit 16. The power amplifier circuit 16 is configured to amplify an RF signal 24 based on the modulated voltage V_(CC).

Notably, there may be an internal routing distance from the power amplifier input 22 to an actual voltage input 26 (e.g., a collector node) of the power amplifier circuit. Given that the internal routing distance is far shorter than the conductive path 18, the internal routing distance is thus neglected hereinafter. Accordingly, the power amplifier input 22 as illustrated herein can be equated with the actual voltage input 26 of the power amplifier circuit 16.

The power management circuit 12 may be coupled to a transceiver circuit 28. Herein, the transceiver circuit 28 is configured to generate the RF signal 24 and the modulated target voltage V_(TGT).

The voltage ripple V_(CC-RP) can be quantitively analyzed based on an equivalent electrical model of the power management circuit 12. In this regard, FIG. 1B is a schematic diagram of an exemplary equivalent electrical model 30 of the power management circuit 12 in FIG. 1A. Common elements between FIGS. 1A and 1B are shown therein with common element numbers and will not be re-described herein.

The ETIC 14 inherently has an inductive impedance Z_(ETIC) that can be modeled by an ETIC inductance L_(ETIC). The conductive path 18 can also be associated with an inductive trace impedance Z_(TRACE) that can be modeled by a trace inductance L_(TRACE). As a result, looking from the power amplifier input 22 toward the ETIC 14, the power amplifier circuit 16 will see an output impedance Z_(OUT) that includes both the inductive impedance Z_(ETIC) and the inductive trace impedance Z_(TRACE).

The power amplifier circuit 16 can be modeled as a current source. In this regard, the power amplifier circuit 16 will modulate a load current I_(LOAD) based on the modulated voltage V_(CC). The load current I_(LOAD) can interact with the output impedance Z_(OUT) to create the voltage ripple V_(CC-RP) in the modulated voltage V_(CC) received at the power amplifier input 22. In this regard, the voltage ripple V_(CC-RP) is a function of the modulated load current I_(LOAD) and the output impedance Z_(OUT), as expressed in equation (Eq. 1) below.

V _(CC-RP) =I _(LOAD) *Z _(OUT)  (Eq. 1)

Notably from the equation (Eq. 1), it may be possible to reduce the voltage ripple V_(CC-RP) by lowering the output impedance Z_(OUT) seen at the power amplifier input 22. In this regard, the conventional approach for reducing the voltage ripple V_(CC-RP) in the power management circuit 12 of FIG. 1A is to add a decoupling capacitor C_(PA) inside the power amplifier circuit 16 and be as close to the power amplifier input 22 as possible. By adding the decoupling capacitor C_(PA), the output impedance Z_(OUT) can be simply expressed as in equation (Eq. 2).

Z _(OUT) =Z _(CPA)∥(Z _(ETIC) +Z _(TRACE))  (Eq. 2)

In the equation (Eq. 2), Z_(CPA) represents a capacitive impedance of the decoupling capacitor C_(PA). The capacitive impedance Z_(CPA) and the inductive impedance Z_(ETIC) and Z_(TRACE) can each be determined according to equations (Eq. 3.1-3.3) below.

|Z _(CPA)|=1/2πf*C _(PA)  (Eq. 3.1)

|Z _(ETIC)|=2πf*L _(ETIC)  (Eq. 3.2)

|Z _(TRACE)|=2πf*L _(TRACE)  (Eq. 3.3)

In the equations (Eq. 3.1-3.3), f represents the modulation frequency of the load current I_(LOAD). In this regard, the capacitive impedance Z_(CPA), the inductive impedance Z_(ETIC), and the inductive trace impedance Z_(TRACE) are each a function of the modulation frequency f. FIG. 1C is a graphic diagram providing an exemplary illustration of magnitude impedance vs. the modulation frequency f.

When the modulation frequency f is lower than 10 MHz, the output impedance Z_(OUT) is dominated by a real part of the inductive impedance Z_(ETIC) and a real part of the inductive trace impedance Z_(TRACE). Between 10 MHz and 100 MHz, the output impedance Z_(OUT) is dominated by the inductive impedance Z_(ETIC) and the inductive trace impedance Z_(TRACE). Above 1000 MHz, the output impedance Z_(OUT) will be dominated by the capacitive impedance Z_(CPA).

Herein, a modulation bandwidth BW_(MOD) of the RF signal 24 may fall between 100 MHz and 1000 MHz (e.g., 100-500 MHz). In this frequency range, the output impedance Z_(OUT) will be determined by the output impedance Z_(OUT) as expressed in equation (Eq. 2).

Notably from equations (Eq. 2 and 3.1), the capacitive impedance Z_(CPA), and therefore the output impedance Z_(OUT), will decrease as the capacitance C_(PA) increases. In this regard, the conventional approach for reducing the ripple voltage V_(CC-RP) relies largely on adding the decoupling capacitor C_(PA) with a larger capacitance (e.g., 1 to 2 μF). However, doing so can cause some obvious issues.

Understandably, a rate of change of the modulated voltage V_(CC) (denoted as ΔV_(CC) or dV_(CC)/dt) can be inversely affected by the capacitance of the decoupling capacitor C_(PA), as shown in equation (Eq. 4) below.

ΔV _(CC) =I _(CC) /C _(PA)  (Eq. 4)

In the equation (Eq. 4), I_(CC) represents a low-frequency current (a.k.a. in-rush current) provided by the ETIC 14 when the decoupling capacitor C_(PA) is charged or discharged. In this regard, the larger capacitance the decoupling capacitor C_(PA) has, the larger amount of the low-frequency current I_(CC) would be needed to change the modulated voltage V_(CC) at a required rate of change (ΔV_(CC)) of the modulated voltage V_(CC). As a result, the existing transmission circuit 10 may cause a negative impact on battery life.

If the low-frequency current I_(CC) is kept at a low level to prolong battery life, the existing transmission circuit 10 may have difficulty meeting the required rate of change (ΔV_(CC)) of the modulated voltage V_(CC), particularly when the RF signal 24 is modulated based on orthogonal frequency division multiplexing (OFDM) for transmission in a millimeter wave (mmWave) spectrum. Consequently, the existing transmission circuit 10 may not be able to change the modulated voltage V_(CC) in between OFDM symbols.

On the other hand, if the capacitance of the decoupling capacitor C_(PA) is reduced to help improve the rate of change (ΔV_(CC)) of the modulated voltage V_(CC) and reduce the in-rush current I_(CC), doing so may lead to insufficient reduction of the output impedance Z_(OUT) and, thus, the voltage ripple V_(CC-RP). Hence, it is desirable to sufficiently reduce the ripple voltage V_(CC-RP) within the modulation bandwidth BW_(MOD) concurrent to improving the rate of change (ΔV_(CC)) of the modulated voltage V_(CC) and reducing the in-rush current I_(CC).

FIG. 2 is a schematic diagram of an exemplary power management circuit 32 configured according to an embodiment of the present disclosure to reduce a voltage ripple V_(CC-RP) in a modulated voltage V_(CC) by reducing an output impedance Z_(OUT) presenting at a power amplifier input 34 of a power amplifier circuit 36. Herein, the power amplifier circuit 36 is configured to receive the modulated voltage V_(CC) via a conductive path 38 (e.g., a conductive trace) and amplify an RF signal 40 based on the modulated voltage V_(CC). The power amplifier circuit 36 includes a decoupling capacitor C_(PA). Similar to the decoupling capacitor C_(PA) in the power amplifier circuit 16 in FIG. 1A, the decoupling capacitor C_(PA) is also provided as close to the power amplifier input 34 as possible.

The power management circuit 32 includes an ETIC 42. The ETIC 42 includes a voltage modulation circuit 44. The voltage modulation circuit 44 is configured to generate the modulated voltage V_(CC) at a voltage output 46 based on a modulated target voltage V_(TGT). Herein, the voltage output 46 is coupled to the power amplifier input 34 via the conductive path 38.

Like the power management circuit 12 in FIG. 1A, the decoupling capacitor C_(PA) has a capacitive impedance Z_(CPA), the ETIC 42 inherently has an inductive impedance Z_(ETIC), and the conductive path 38 is inherently associated with an inductive trace impedance Z_(TRACE), which can be expressed as in the equations (Eq. 3.1-3.3). Accordingly, the power amplifier circuit 36 will see an output impedance Z_(OUT), as determined in the equation (Eq. 2), within a modulation bandwidth (e.g., 100-500 MHz) of the RF signal 40. Herein, the power amplifier circuit 36 also operates as a current source, which can induce a modulated load current I_(LOAD) based on the modulated voltage V_(CC). Similar to the power management circuit 12 in FIG. 1A, the modulated load current I_(LOAD) can interact with the output impedance Z_(OUT) to create the voltage ripple V_(CC-RP) in the modulated voltage V_(CC) received at the power amplifier input 34.

In embodiments disclosed herein, the decoupling capacitor C_(PA) has a smaller capacitance (e.g., 100 pF) compared to the decoupling capacitor C_(PA) in the power amplifier circuit 16 in FIG. 1A. By employing the smaller decoupling capacitor C_(PA), it is possible to improve the rate of change (ΔV_(CC)) of the modulated voltage V_(CC) to satisfy the stringing voltage switching time requirement (e.g., per OFDM symbol or sub-symbol) in such advanced wireless systems as fifth generation (5G) and 5G new-radio (5G-NR), while concurrently reducing the in-rush current I_(CC) to prolong battery life.

Further, the power management circuit 32 is configured to reduce the voltage ripple V_(CC-RP) in the modulated voltage V_(CC) by reducing the output impedance Z_(OUT) presenting at the power amplifier input 34 and/or creating a notch filter at the power amplifier input 34. As a result, the power management circuit 32 can achieve a defined performance threshold, such as RMS EVM and/or peak EVM within the modulation bandwidth of the RF signal 40.

In an embodiment, the voltage modulation circuit 44 includes a voltage amplifier 48 (denoted as “VA”), which can be an operational amplifier (OpAmp), as an example. The voltage amplifier 48 is configured to generate an initial modulated voltage V_(AMP) at a voltage amplifier output 50 based on the modulated target voltage V_(TGT) and a supply voltage V_(SUP). The voltage modulation circuit 44 also includes an offset capacitor C_(OFF) that is coupled in between the voltage amplifier output 50 and the voltage output 46. The offset capacitor C_(OFF) is configured to raise the initial modulated voltage V_(AMP) by an offset voltage V_(OFF) to thereby generate the modulated voltage V_(CC) at the voltage output 46 (V_(CC)=V_(AMP)+V_(OFF)).

The voltage amplifier 48 is also configured to receive a modulated voltage feedback V_(CC-FB) that indicates the modulated voltage V_(CC) at the voltage output 46, thus making the voltage modulation circuit 44 a closed-loop circuit. Accordingly, the voltage amplifier 48 can adjust the initial modulated voltage V_(AMP) and, thus the modulated voltage V_(CC), based on the modulated feedback V_(CC-FB) to better track the modulated target voltage V_(TGT).

The voltage amplifier 48 includes an input/bias stage 52 and an output stage 54. The output stage 54 is coupled in series to the voltage amplifier output 50. According to an embodiment of the present disclosure, the output stage 54 is configured to receive a power amplifier voltage feedback V_(CC-PA-FB) that indicates the modulated voltage V_(CC) as received at the power amplifier input 34. In an embodiment, the output stage 54 may receive the power amplifier voltage feedback V_(CC-PA-FB) via a feedback path 56. Like the conductive path 38, the feedback path 56 is associated with an inductive feedback trace impedance Z_(TRACE-FB) that can be modeled by a feedback inductance L_(TRACE-FB).

Understandably, since the power amplifier voltage feedback V_(CC-PA-FB) is provided from the power amplifier input 34, the power amplifier voltage feedback V_(CC-PA-FB) will include the voltage ripple V_(CC-RP) in the modulated voltage V_(CC) as received at the power amplifier input 34. Accordingly, the voltage amplifier 48 may modify the initial modulated voltage V_(AMP) based on the power amplifier voltage feedback V_(CC-PA-FB) to cause the output impedance Z_(OUT) to be reduced at the power amplifier input 34, thus helping to reduce the voltage ripple V_(CC-RP) in the modulated voltage V_(CC) that is received at the power amplifier input 34.

The ETIC 42 may include a control circuit 58, which can be a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC), as an example. In an embodiment, the control circuit 58 may control the voltage amplifier 48, for example, via a control signal 60, to modify the initial modulated voltage V_(AMP) based on the power amplifier voltage feedback V_(CC-PA-FB) to thereby reduce the output impedance Z_(OUT) at the power amplifier input 34.

FIG. 3 is a schematic diagram providing an exemplary illustration of an inner structure of the voltage amplifier 48 in FIG. 2 . Common elements between FIGS. 2 and 3 are shown therein with common element numbers and will not be re-described herein.

In an embodiment, the input/bias stage 52 is configured to receive the modulated target voltage V_(TGT) and the modulated voltage feedback V_(CC-FB). Accordingly, the input/bias stage 52 generates a pair of bias signals 62P, 62N to control the output stage 54.

In an embodiment, the output stage 54 is configured to generate the initial modulated voltage V_(AMP) at the voltage amplifier output 50 based on a selected one of the bias signals 62P, 62N. The output stage 54 is also configured to receive the power amplifier voltage feedback V_(CC-PA-FB). Accordingly, the output stage 54 can modify the initial modulated voltage V_(AMP) based on the power amplifier voltage feedback V_(CC-PA-FB) to reduce the output impedance Z_(OUT) and thereby the voltage ripple V_(CC-RP) at the power amplifier input 34.

In an embodiment, the output stage 54 includes a first transistor 64P and a second transistor 64N. In a non-limiting example, the first transistor 64P is a p-type field-effect transistor (pFET) and the second transistor 64N is an n-type FET (nFET). In this example, the first transistor 64P includes a first source electrode S1, a first drain electrode D₁, and a first gate electrode G₁, and the second transistor 64N includes a second source electrode S2, a second drain electrode D₂, and a second gate electrode G₂. Specifically, the first drain electrode D₁ is configured to receive the supply voltage V_(SUP), the second drain electrode D₂ is coupled to a ground (GND), and the first source electrode S1 and the second source electrode S2 are both coupled to the voltage amplifier output 50.

The first gate electrode G₁ is coupled to the input/bias stage 52 to receive the bias signal 62P and the second gate electrode G₂ is coupled to the input/bias stage 52 to receive the bias signal 62N. Herein, the input/bias stage 52 is configured to generate the bias signal 62P in response to an increase of the modulated voltage V_(CC) or generate the bias signal 62N in response to a decrease of the modulated voltage V_(CC). Specifically, the first transistor 64P will be turned on to output the initial modulated voltage V_(AMP) and source a high-frequency current I_(AC) (e.g., an alternating current) from the supply voltage V_(SUP) in response to receiving the bias signal 62P, and the second transistor 64N will be turned on to output the initial modulated voltage V_(AMP) from the supply voltage V_(SUP) and sink the high-frequency current I_(AC) to the GND in response to receiving the bias signal 62N.

In this embodiment, the output stage 54 also includes a first Miller capacitor C_(Miller1) and a second Miller capacitor C_(Miller2). Specifically, the first Miller capacitor C_(Miller1) is coupled between the voltage amplifier output 50 and the first gate electrode G₁, and the second Miller capacitor C_(Miller2) is coupled between the voltage amplifier output 50 and the second gate electrode G₂. In this regard, the output stage 54 can be regarded as a typical class AB rail-rail OpAmp output stage. The first Miller capacitor C_(Miller1) and the second Miller capacitor C_(Miller2) not only can stabilize controls of the first transistor 64P and the second transistor 64N (e.g., mitigating so-called Miller effect), but may also reduce the closed-loop output impedance of the voltage amplifier 48.

Notably, since the first Miller capacitor C_(Miller1) and the second Miller capacitor C_(Miller2) are each coupled to the voltage amplifier output 50, the first Miller capacitor C_(Miller1) and the second Miller capacitor C_(Miller2) can only reduce the inductive impedance Z_(ETIC), which is part of the output impedance Z_(OUT) seen at the power amplifier input 34. As such, to further reduce the output impedance Z_(OUT), it is also necessary to reduce the inductive trace impedance Z_(TRACE).

In this regard, the output stage 54 further includes a first resistor-capacitor (RC) circuit 66P and a second RC circuit 66N. The first RC circuit 66P and the second RC circuit 66N are both coupled to the power amplifier input 34 via the feedback path 56 to thereby receive the power amplifier voltage feedback V_(CC-PA-FB). Specifically, the first RC circuit 66P is coupled between the power amplifier input 34 and the first gate electrode G₁, and the second RC circuit 66N is coupled between the power amplifier input 34 and the second gate electrode G₂. As such, the first RC circuit 66P can cause the power amplifier voltage feedback V_(CC-PA-FB) to be combined with the bias signal 62P to thereby modify the bias signal 62P. Similarly, the second RC circuit 66N can cause the power amplifier voltage feedback V_(CC-PA-FB) to be combined with the bias signal 62N to thereby modify the bias signal 62N.

In an embodiment, the first RC circuit 66P includes a first adjustable resistor R_(FB1) and a first adjustable capacitor C_(FB1), and the second RC circuit 66N includes a second adjustable resistor R_(FB2) and a second adjustable capacitor C_(FB2). Recall that the feedback path 56 is associated with the inductive feedback trace impedance Z_(TRACE-FB) that can be modeled by the feedback inductance L_(TRACE-FB). As such, the first adjustable resistor R_(FB1), the first adjustable capacitor C_(FB1), and the feedback inductance L_(TRACE-FB) can be equated with a first resistor-inductor-capacitor (RLC) circuit, which has a first resonance frequency f₁ as expressed in equation (Eq. 5) below.

f ₁=1/2π√{square root over (L _(TRACE-FB) *C _(FB1))}  (Eq. 5)

Likewise, the second adjustable resistor R_(FB2), the second adjustable capacitor C_(FB2), and the feedback inductance L_(TRACE-FB) can be equated with a second RLC circuit, which has a second resonance frequency f₂ as expressed in equation (Eq. 6) below.

f ₂=1/2π√{square root over (L _(TRACE-FB) *C _(FB2))}  (Eq. 6)

From equations (Eq. 5 and 6), the first adjustable capacitor C_(FB1) and the second adjustable capacitor C_(FB2) can each be adjusted to resonate with the feedback inductance L_(TRACE-FB) to create a low-impedance feedback path at a respective one of the first resonance frequency f₁ and the second resonance frequency f₂. The first adjustable resistor R_(FB1) will de-Q (i.e., decrease Q-factor) the first resonance frequency f₁ across the modulation bandwidth BW_(MOD) to prevent the first adjustable capacitor C_(FB1) and the feedback inductance L_(TRACE-FB) from entering oscillation at the first resonance frequency f₁. Likewise, the second adjustable resistor R_(FB2) will de-Q (i.e., decrease Q-factor) the second resonance frequency f₂ across the modulation bandwidth BW_(MOD) to prevent the second adjustable capacitor C_(FB2) and the feedback inductance L_(TRACE-FB) from entering oscillation at the second resonance frequency f₂.

When the voltage ripple V_(CC-RP) seen at the power amplifier input 34 is fed back to the first gate electrode G₁ or the second gate electrode G₂, the first transistor 64P and the second transistor 64N may act like a common source amplifier, which amplifies and inverts the initial modulated voltage V_(AMP) at the voltage amplifier output 50 and, therefore, the voltage output 46 of the ETIC 42. The inverted initial modulated voltage V_(AMP) will cause more of the load current I_(LOAD) to flow to the GND through the conductive path 38 (a.k.a. the trace inductor L_(TRACE)) than flowing through the power amplifier circuit 36, thus lowering the inductive trace impedance Z_(TRACE) and, accordingly the output impedance Z_(OUT) at the power amplifier input 34.

Thus, by adjusting the first adjustable capacitor C_(FB1), the first adjustable resistor R_(FB1), the second adjustable capacitor C_(FB2), and/or the second adjustable resistor R_(FB2), it is possible to reduce the output impedance Z_(OUT) across the modulation bandwidth BW_(MOD). In an embodiment, the first adjustable capacitor C_(FB1), the first adjustable resistor R_(FB1), the second adjustable capacitor C_(FB2), and/or the second adjustable resistor R_(FB2) may be adjusted by the control circuit 58 via the control signal 60.

By employing the first Miller capacitor C_(Miller1) and the second Miller capacitor C_(Miller2) to help reduce the inductive impedance Z_(ETIC), and further employing the first RC circuit 66P and the second RC circuit 66N to help reduce the inductive trace impedance Z_(TRACE), it is possible to reduce the output impedance Z_(OUT) to thereby reduce the voltage ripple V_(CC-RP) in the modulated voltage V_(CC). A simulation shows that, at 200 MHz load current modulation frequency, the power management circuit 32 can reduce an RMS value of the voltage ripple V_(CC-RP) from 231 mV, as in the power management circuit 12 in FIG. 1A, to 134 mV, which amounts to a 42% improvement.

With reference back to FIG. 2 , the ETIC 42 further includes a switcher circuit 68. In an embodiment, the switcher circuit 68 includes a multi-level charge pump (MCP) 70 that is coupled to the voltage output 46 via a power inductor L_(P). The MCP 70, which can be a buck-boost voltage converter, as an example, is configured to generate a low-frequency voltage V_(DC) based on a battery voltage V_(BAT). Specifically, the MCP 70 may operate in a buck mode to generate the low-frequency voltage V_(DC) at 0×V_(BAT) or 1×V_(BAT), or in a boost mode to generate the low-frequency voltage V_(DC) at 2×V_(BAT). Thus, by configuring the MCP 70 to toggle between 0×V_(BAT), 1×V_(BAT), and/or 2×V_(BAT) based on an appropriate duty cycle, the MCP 70 can generate the low-frequency voltage V_(DC) at multiple voltage levels.

The power inductor L_(P) is configured to induce a low-frequency current I_(CC) (a.k.a. in-rush current) based on the low-frequency voltage V_(DC). As previously described in FIG. 1A, the low-frequency current I_(CC) is provided to the power amplifier input 34 to charge the decoupling capacitor C_(PA).

In addition to reducing the output impedance Z_(OUT) to help reduce the voltage ripple V_(CC-RP), it is possible to further reduce the voltage ripple V_(CC-RP) at a specific load current modulation frequency within the modulation bandwidth of the RF signal 40 using a notch filter. In this regard, FIG. 4 is a schematic diagram of an exemplary power management circuit 72, wherein a notch circuit 74 can be added to the power management circuit 32 of FIG. 2 to further reduce the voltage ripple V_(CC-RP) in the modulation voltage V_(CC). Common elements between FIGS. 2 and 4 are shown therein with common element numbers and will not be re-described herein.

The power management circuit 72 includes an ETIC 76, wherein the notch circuit 74 is provided. It should be appreciated that it is also possible for the notch circuit 74 to be integrated into the power amplifier circuit 36. Herein, the notch circuit 74 is coupled to the power amplifier input 34 via a notch path 78. Like the conductive path 38 and the feedback path 56, the notch path 78 is also associated with an inductive notch trace impedance Z_(TRACE-N) that can be modeled by a notch inductance L_(TRACE-N). In an embodiment, the notch circuit 74 may be controlled by the control circuit 58, for example via a second control signal 80, to resonate at a notch frequency f_(NOTCH) within the modulation bandwidth BW_(MOD) to reduce the voltage ripple V_(CC-RP) in the modulated voltage V_(CC). In an embodiment, the notch frequency f_(NOTCH) may be determined by factoring in the notch inductance L_(TRACE-N) associated with the notch path 78. As a result, the power management circuit 72 can achieve a defined performance threshold (e.g., RMS EVM or peak EVM). A simulation shows that, by adding the notch circuit 74 into the power management circuit 32 of FIG. 2 , the RMS value of the voltage ripple V_(CC-RP) can be further reduced from 134 mV to 87 mV for the 200 MHz load current modulation frequency.

FIG. 5 is a schematic diagram illustrating an exemplary configuration of the notch circuit 74 in the power management circuit 72 of FIG. 4 . Common elements between FIGS. 4 and 5 are shown therein with common element numbers and will not be re-described herein.

Herein, the notch circuit 74 includes a notch capacitor C_(NOTCH), a notch inductor L_(NOTCH), and a switch circuit 82. The switch circuit 82 includes multiple switches S_(N1)-S_(NN), each having a respective one of multiple notch resistances R_(N1)-R_(NN). Notably, the notch resistances R_(N1)-R_(NN) can be identical to or different from one another. The notch inductor L_(NOTCH) includes multiple tap points TP₁-TP_(N), each corresponding to a respective one of multiple notch inductances L_(N1)-L_(NN). Herein, each of the notch switches S_(N1)-S_(NN) is coupled between a respective one of the tap points TP₁-TP_(N) and the GND. Thus, by selectively closing any one of the notch switches S_(N1)-S_(NN), it is possible to change the overall resistance and inductance of the notch circuit 74 and, therefore, change the notch frequency f_(NOTCH) of the notch circuit 74.

In an embodiment, the control circuit 58 may control the switch circuit 82 via the second control signal 80 to selectively close any of the notch switches S_(N1)-S_(NN). In a non-limiting example, the notch resistances R_(N1)-R_(NN), the notch inductances L_(N1)-L_(NN), the notch inductance L_(TRACE-N), and the notch capacitance C_(NOTCH) can be determined experimentally and/or empirically based on a target modulation of the load current I_(LOAD) to ensure that the notch frequency f_(NOTCH) falls within the modulation bandwidth BW_(MOD) and the voltage ripple V_(CC-RP) can be minimized. For example, when the modulation bandwidth BW_(MOD) is 200 MHz, the RMS value of the voltage ripple V_(CC-RP) can be reduced to 87 mV by setting the notch capacitance C_(NOTCH) to 300 pF, the notch resistance R_(X) (1≤X≤N) to 1Ω, and the notch inductance L_(X) (1≤X≤N) to 4 nH.

The power management circuit 32 of FIG. 2 and the power management circuit 72 of FIG. 4 can be provided in a user element to enable bandwidth adaptation according to embodiments described above. In this regard, FIG. 6 is a schematic diagram of an exemplary user element 100 wherein the power management circuit 32 of FIG. 2 and the power management circuit 72 of FIG. 4 can be provided.

Herein, the user element 100 can be any type of user elements, such as mobile terminals, smart watches, tablets, computers, navigation devices, access points, and like wireless communication devices that support wireless communications, such as cellular, wireless local area network (WLAN), Bluetooth, and near field communications. The user element 100 will generally include a control system 102, a baseband processor 104, transmit circuitry 106, receive circuitry 108, antenna switching circuitry 110, multiple antennas 112, and user interface circuitry 114. In a non-limiting example, the control system 102 can be a field-programmable gate array (FPGA), as an example. In this regard, the control system 102 can include at least a microprocessor(s), an embedded memory circuit(s), and a communication bus interface(s). The receive circuitry 108 receives radio frequency signals via the antennas 112 and through the antenna switching circuitry 110 from one or more base stations. A low noise amplifier and a filter cooperate to amplify and remove broadband interference from the received signal for processing. Downconversion and digitization circuitry (not shown) will then downconvert the filtered, received signal to an intermediate or baseband frequency signal, which is then digitized into one or more digital streams using analog-to-digital converter(s) (ADC).

The baseband processor 104 processes the digitized received signal to extract the information or data bits conveyed in the received signal. This processing typically comprises demodulation, decoding, and error correction operations, as will be discussed in greater detail below. The baseband processor 104 is generally implemented in one or more digital signal processors (DSPs) and application specific integrated circuits (ASICs).

For transmission, the baseband processor 104 receives digitized data, which may represent voice, data, or control information, from the control system 102, which it encodes for transmission. The encoded data is output to the transmit circuitry 106, where a digital-to-analog converter(s) (DAC) converts the digitally encoded data into an analog signal and a modulator modulates the analog signal onto a carrier signal that is at a desired transmit frequency or frequencies. A power amplifier will amplify the modulated carrier signal to a level appropriate for transmission, and deliver the modulated carrier signal to the antennas 112 through the antenna switching circuitry 110. The multiple antennas 112 and the replicated transmit and receive circuitries 106, 108 may provide spatial diversity. Modulation and processing details will be understood by those skilled in the art.

Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow. 

What is claimed is:
 1. A power management circuit comprising: a power amplifier circuit configured to amplify a radio frequency (RF) signal based on a modulated voltage received at a power amplifier input, wherein the modulated voltage received at the power amplifier input comprises a voltage ripple caused by an output impedance presenting at the power amplifier input and a load current induced by the modulated voltage; and an envelope tracking integrated circuit (ETIC) coupled to the power amplifier input via a conductive path and comprising: a voltage modulation circuit configured to generate the modulated voltage at a voltage output based on a modulated target voltage; and a notch circuit coupled to the power amplifier input via a notch path and configured to resonate at a notch frequency within a modulation bandwidth of the RF signal to reduce the voltage ripple to thereby achieve a defined performance threshold.
 2. The power management circuit of claim 1, wherein the ETIC further comprises a control circuit configured to determine the notch frequency and cause the notch circuit to resonate at the notch frequency.
 3. The power management circuit of claim 2, wherein the control circuit is further configured to determine the notch frequency based on a target modulation of the load current within the modulation bandwidth of the RF signal to thereby minimize a root-mean-square (RMS) error vector magnitude (EVM) at the target modulation.
 4. The power management circuit of claim 2, wherein the control circuit is further configured to determine the notch frequency based on a target modulation of the load current within the modulation bandwidth of the RF signal to thereby minimize a peak error vector magnitude (EVM) at the target modulation.
 5. The power management circuit of claim 2, wherein the control circuit is further configured to determine the notch frequency to factor in a notch inductance associated with the notch path.
 6. The power management circuit of claim 2, wherein the notch circuit comprises: a notch capacitor coupled to the power amplifier input; a notch inductor comprising a plurality of tap points each corresponding to a respective one of a plurality of notch inductances; and a plurality of notch switches each coupled between a respective one of the plurality of tap points and a ground.
 7. The power management circuit of claim 6, wherein the control circuit is further configured to close a selected one of the plurality of notch switches to thereby cause the notch circuit to resonate at the determined notch frequency.
 8. The power management circuit of claim 1, wherein the voltage modulation circuit is coupled to the power amplifier input via a feedback path and further configured to: receive power amplifier voltage feedback indicating the voltage ripple in the modulated voltage received at the power amplifier input; and modify the modulated voltage based on the power amplifier voltage feedback to cause a reduction in the output impedance to thereby reduce the voltage ripple in the modulated voltage received at the power amplifier input.
 9. The power management circuit of claim 8, wherein the voltage modulation circuit comprises: a voltage amplifier configured to generate an initial modulated voltage at a voltage amplifier output based on the modulated target voltage and a supply voltage; and an offset capacitor coupled between the voltage amplifier output and the voltage output and configured to raise the initial modulated voltage by an offset voltage to thereby generate the modulated voltage at the voltage output.
 10. The power management circuit of claim 9, wherein the voltage amplifier is further configured to: receive the power amplifier voltage feedback indicating the voltage ripple at the power amplifier input; and modify the initial modulated voltage based on the indicated voltage ripple to thereby reduce the voltage ripple in the modulated voltage.
 11. The power management circuit of claim 10, wherein the voltage amplifier comprises: an input/bias stage configured to generate a pair of bias signals based on the modulated target voltage and feedback of the modulated voltage; and an output stage configured to generate the initial modulated voltage based on a selected one of the pair of bias signals.
 12. The power management circuit of claim 11, wherein the output stage is further configured to: receive the power amplifier voltage feedback indicating the voltage ripple at the power amplifier input; and modify the initial modulated voltage based on the indicated voltage ripple to thereby reduce the voltage ripple in the modulated voltage.
 13. The power management circuit of claim 12, wherein the output stage comprises: a first transistor having a first drain electrode configured to receive the supply voltage, a first source electrode coupled to the voltage amplifier output, and a first gate electrode configured to receive a positive one of the pair of bias signals; and a second transistor having a second drain electrode coupled to a ground, a second source electrode coupled to the voltage amplifier output, and a second gate electrode configured to receive a negative one of the pair of bias signals.
 14. The power management circuit of claim 13, wherein the first transistor is a p-type field-effect transistor (pFET) and the second transistor is an n-type field-effect transistor (nFET).
 15. The power management circuit of claim 13, wherein: the first transistor is further configured to source a high-frequency current from the supply voltage in response to receiving the positive one of the pair of bias signals; and the second transistor is further configured to sink the high-frequency current from the voltage output to the ground in response to receiving the negative one of the pair of bias signals.
 16. The power management circuit of claim 13, wherein the output stage further comprises: a first Miller capacitor coupled between the voltage amplifier output and the first gate electrode; and a second Miller capacitor coupled between the voltage output and the second gate electrode.
 17. The power management circuit of claim 16, wherein the first Miller capacitor and the second Miller capacitor are configured to reduce the output impedance presenting at the power amplifier input.
 18. The power management circuit of claim 13, wherein the output stage further comprises: a first resistor-capacitor circuit coupled between the power amplifier input and the first gate electrode of the first transistor; and a second resistor-capacitor circuit coupled between the power amplifier input and the second gate electrode of the second transistor.
 19. The power management circuit of claim 18, wherein: the first resistor-capacitor circuit is configured to: receive the power amplifier voltage feedback via the feedback path; and modify the positive one of the pair of bias signals based on the voltage ripple indicated in the power amplifier voltage feedback; and the second resistor-capacitor circuit is configured to: receive the power amplifier voltage feedback via the feedback path; and modify the negative one of the pair of bias signals based on the voltage ripple indicated in the power amplifier voltage feedback.
 20. The power management circuit of claim 19, wherein each of the first resistor-capacitor circuit and the second resistor-capacitor circuit comprises a respective adjustable capacitor and a respective adjustable resistor that can be adjusted to reduce the output impedance presenting at the power amplifier input. 